text:
Does the bottom rotor on a Coaxial quadcopter spin faster?
On the typical setup of a coaxial quadcopter, does the bottom rotor spin at a higher rpm than the top rotor? Or does it have different pitch, or is it exactly the same as the top rotor?

source

To reduce cost, quadcopters reduce how many different parts they have.  So on each arm, the upper and lower motors are usually the same, as are the "rotors" (propellers;  making a cw/ccw pair that is an exact mirror image is cheaper).  So each arm's top rotor and bottom rotor share the same RPM:  the flight controller software that converts pilot commands to individual motor speeds is typically the same for one or for two motors per arm.
For efficiency, the downstream prop's RPM, pitch, and diameter should correct for the propwash that it's in.  But that optimization's worthwhile only for much larger, more expensive setups.

Packing List. Motors: 8 Pieces

If they used only four motors they would need gearboxes to invert the direction of one of the rotors in the coax pair. For many applications, the choice between "motor or gearbox" is a no-brainer with gears being cheaper, able to handle more torque and being needed anyways. I suppose drones are an exception, because the rotors spin at extremely high RPM.

Reversing such a "BLDC" motor needs no gearbox.  You just swap two of the three wires that power it from its "ESC" electronic speed controller.

@CamilleGoudeseune if you only want to use 4 motors you need to use gearboxes...

Ah, I misunderstood.  Y'all mean one motor driving two contrarotating propellors.  Yeah, that needs gears.

@leftaroundabout "being needed anyways"...what you mean by that?

@Gabe lots of applications need a gearbox for reasons unrelated to direction-inversion (most typically to get more torque). If you have a gearbox anyways then there is no point adding an extra motor to avoid using gears to invert direction.

If one motor is loaded with less torque, it will naturally spin faster. This doesn't exactly result in equal lift from the two motors or equal power, but it compensates the propwash effect at least partially.
Quadcopter motors are usually voltage controlled (actually fixed voltage + pwm). Only the voltage is actively controlled, the other parameters (rpm, torque, power, current) then settle on some equilibrium. If one motor is loaded with less torque, it will naturally spin faster. The flight controller will usually send the same throttle setting (pwm value) to both motors. There is no active compensation for propwash effect.
If you build a coaxial quadcopter, you can use different propellers for top and bottom, e.g. 5x3" and 5x4". That's your choice and you may indeed get better performance compared to identical propellers. You don't have to worry about adjusting rpm because each motor/propeller combination will find its own equilibrium.

These are almost universally brushless DC motors. They spin exactly as fast as they are commanded to.

@EugeneRyabtsev - No, BLDC motors are not commanded to spin at a certain RPM, otherwise they'd be synchronous AC motors. BLDC Motors have exactly the behavior described in my answer.

They exhibit that behavior in open-loop control system only. Is there normally one loop per motor or one loop per pair?

@EugeneRyabtsev - The 8-motor quadcopter still has only four control loops (roll, pitch, yaw, collective). The feedback signals for those loops come from gyro/accelerometer/altimeter. There is no RPM feedback, hence open loop control with respect to RPM.

Packing List. ESC: 8 Pieces

Meaning those loops. I assume some sensing per motor (either back EMF or direct).

@EugeneRyabtsev - Yes, that's what I told you. 8 motors on 8 separate ESCs -> each motor/propeller/esc will find its own equilibrium RPM. The flight controller only sends throttle commands to the ESCs, not RPM commands.

Okay, I might have misunderstood this. Was under the impression it works like this: https://electronics.stackexchange.com/a/255491/29238

I agree with this answer. Usually quadcopter ESCs convert the throttle command to PWM duty cycle, with no explicit RPM regulation loop. The PWM duty cycle will roughly correspond to RPM, but not exactly due to winding resistance and inductance.

@EugeneRyabtsev: Making a BLDC motor spin smoothly at a certain speed requires that one not only drive the commutation waveform at that speed, but also that feeds the motor the right voltage.  If the voltage is too high, the motor will start spinning faster than the commutation speed until the rotor position gets ahead of the rotating magnetic field, and then slow down until the rotor position falls behind the magnetic field, then speed up, then slow down, etc.


text:
Does anyone know why the Horten Ho 229 V2 crashed?
On February 18, 1945 the German Horten Ho 229 crashed due to an engine failure and I was wondering if the failure was caused because of the planes irregular shape or some other external factor. I will also accept plausible theories as an answer.

The little what is known is that one engine cut out and the plane went into a spiral dive from which it could not be recovered. This happened at low altitude so the ejection seat could not save the pilot (and was not activated, as far as I know).
Since Reimar Horten insisted on only a wing and not even adding a vertical tail to his designs, the lateral stability was marginal and control authority only provided by drag devices at the wingtips. Those looked like miniature airbrakes in the Go-229 and comprised a small and a larger brake, which worked well at high speed. At low speed, however, this drag is comparatively low, so control authority suffers.
Heinz Scheidhauer, who had flown all Horten glider designs, once told me that at higher speed, without the help of induced drag on the swept wing, the Horten gliders would "swim", meaning they yawed left and right when hit by gusts. You had to get used to this - eventually the yawing motion would die down in calm air.
In my opinion, the asymmetric thrust could not be compensated by the pilot with the little control authority he had at his disposal. Only the addition of a vertical tail and a rudder could had avoided that accident. Not adding this has made the Go-229 a deathtrap.

the Horten Ho 229 crashed due to an engine failure and I was wondering if the failure was caused because of the planes irregular shape or some other external factor.

Without a post-flight report it's hard to give an answer. Anyway everything points to an inherent problem at the engine itself not directly related to the plane's shape or some other external factor (source Wikipedia):
"It was not until early 1944 that full production could finally begin... Given the lower-quality steels used in the 004B, these engines had a service life of only 10–25 hours, perhaps twice this in the hands of a careful pilot. Another shortcoming of the engine, common to all early turbojets, was its sluggish throttle response. Worse, too much fuel could be injected into the combustion chambers by moving the throttle too quickly, causing the temperature to rise too far before the airflow increased to match the increased fuel. This overheated the turbine blades, and was a major cause for engine failures... Completed engines earned a reputation for unreliability; the time between major overhauls was thirty to fifty hours, and may have been as low as ten... The process involved replacing compressor blades, (which suffered the most damage, usually from ingesting stones and such, later known as fodding) and turbine blades damaged by the high thermodynamic loads"

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
drag force relationship with cube of speed?
So I saw this physics website that said drag grows quadratically with speed. Meaning the drag force at 200 km/h is 4 times what it is at 100 km/h. Ok I'm fine with that. But then it said the work required to accelerate to that speed grows cubically. Meaning I need 8 times the power to accelerate from 100 km/h to 200km/h? this part I dont get.
So if my imaginary engine was producing x kilowatts or kilonewtons, and I pressed a button and its now doing 4x:

Isnt it logical that I should accelerate if I am going only 100 km/h, since drag isnt 4x yet??
Shouldnt I keep accelerating until equilibrium out at 200 km/h?

Update: the power vs force distinction solves it. I was mislead by the use of the word "accelerate" in that page. I thought it was discussion about drag and acceleration. There is no accelerate. The power required to go from A to B in half the time is 2x larger. And drag grows quadratically.

Does this answer your question? How much power is needed to drive two times faster? - From Review

You seem to be confusing force (thrust or drag) with energy (under which concept work and power comes). Don't. You'll be spared much grief.
Work done is force times distance.
$$ W = Fs $$
Power is work done divided by time
$$ P = W/t $$
When you double velocity, force quadruples. As does work.
$$ W_\text{new} = 4Fs = 4W $$
Time halves as well, with the following effect on power.
$$ P_\text{new} = 4W/0.5t = 8P $$

Whoever just edited. Make a superficial edit again so your name can be seen. You're the victim of an unfortunate coincidence

No need to see my name (it is still in the edit history) ;)

power vs force solves it. I was missing the distinction. yes drag force goes up with the square, but power goes up another 2x because times goes down 2x.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can I (holding a private pilots license) fly other employees of my company?
I am an HR manager and my job in no way counts on me for flying. I have my private pilots license and a second class medical. If I on occasion fly a company owned aircraft with other employees on it to a fire is that considered “Incidental” under FAR 61.113 (B)(1)?  I would get no bonuses for this and it would fall during normal business hours .

I'm curious about the "to a fire" part of your question. Would this be part of an emergency response? What hazards would involved in the flight? Is there sufficient time for flight planning, particularly for contingencies? I don't know the answer to your question for certain, but it seems very much like this would not be permitted under the "private" license conditions.

You can fly yourself to any business-related function you want and that would be considered "incidental".  As soon as you take paperwork, other employees, other business items, etc. it becomes a question of whether or not you are acting as an air carrier or commercial operator.
61.113 specifically forbids the carriage of passengers or property on these incidental business trips.
I understand there is a clause here about compensation or hire.
The FAA interprets that clause very broadly.  See Sommer Interpretation (2010)
I would say not having to do your work while piloting a plane could be considered a form of compensation.  I would not take such a chance in your position.

The Sommer interpretation doesn't cover this.

I’m not sure about the “not doing your job” here counts as compensation.  The common test for “incidental” flight is whether you’d also get paid if you drove instead.

Your must ask FAA, they are more than happy to advice you on this matter. I (as well as anybody else here on ASE) have no power to rule on this particular case.
This is not as straightforward as it seems at first glance. The flight would be incidental to your business/work for sure. You would get paid for travelling* regardless of the transport method, so would the passengers. I'm assuming your pay does not change as a result of flying yourself, or taking colleagues as passenger, or transporting business related items.

(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:
(1) The flight is only incidental to that business or employment; and
(2) The aircraft does not carry passengers or property for compensation or hire.

(emphasis mine)
So as long as the flight would yield no financial benefit to you it would seem allright. However, also the situation of your employer should be evaluated, as it would benefit from not having to pay for the transport of your colleagues. Not a simple equation at all...
So it's well worth asking the FAA, unless someone comes up with a case that is an exact match to yours.
*depending on your company policy of course

Note that the FAA interprets "compensation" extremely broadly. For example, in the decision linked in wbeard52's answer, a dinner invitation is considered "compensation". And if I remember correctly, it was mentioned in some discussions here on the site that even the fact that the PIC can log hours can be considered compensation if they had otherwise not flown if there hadn't been passengers.

@JörgWMittag yep, hence the strong recommemdation to ask FAA, not the internet.

And even if you somehow got a favorable interpretation from the FSDO or a case precedent, they could still nail you later in court if they can find any little detail that deviates from the scenario considered in the FSDO letter / other case. My own advice would be don't do it and don't waste time asking the FAA - no matter their answer you are putting yourself in an uncomfortable legal position in the event of an incident.

No, according to the Mangiamele Letter, which is an FAA interpretation of rules, you cannot ask for reimbursement for a business flight if you take passengers:

In regard to whether you may seek reimbursement from your employer for
transporting your colleagues, since you are transporting people to the
meeting, the allowance for the flight to be conducted for compensation
or hire (i.e., reimbursement) under 61. l 13(b) does not apply. The
exception in paragraph (b) allows you to use your private pilot
certificate only for compensation or hire if the operation is
incidental to your employment and you are not transporting other
passengers or property. Thus, because you are transporting people to
the meeting, you may not seek reimbursement from your employer for
this flight under 14 C.F.R. § 61.113(b).

So in the FAA jurisdiction you would only be able to share costs if you take your colleagues, but if you fly yourself you could be reimbursed.
This isn't universal across the world, in the UK you can take colleagues. So it partly depends on where you are.

" it would fall during normal business hours "
Which means you effectively would get paid for flying them, which is a big nono for a PPL holder. You'd need at least a CPL.
Were you to fly them outside of your normal working hours and not be paid overtime for it, it MIGHT be ok though the cost of the aircraft, parking, and fuel might still be considered payment (I am not sure about that, though some bureaucrat is likely to try that).

I am not sure this hold. One could argue that the employee is being paid to compensate for the time they are spending traveling to the business meeting. You are being paid this amount regardless whether you are flying yourself, driving yourself, being flown by someone else or being driven by some else. From this it is clear that you are not being paid for the flying, but just for getting your *ss from A to B.

GdD’s answer contains a ruling from the FAA that specifically allows it in some circumstances (but not others), so this general answer is incorrect or at least incomplete.


text:
How is Horizontal Visibility and RVR related and how does it affect the Low Visibility Operations?
So on my foggy landing  the METAR 9 minutes before the touchdown stated Horizontal Visibility as 0000 and RVR 100
whereas the metar 21 minutes after my landing stated Horizontal Visibility 0100 and RVR 750
Now when I landed the visibility was very poor even the runway borderline were blurred by fog for the much part of rolldowm however,I could see around 46 to 50 something meters as per my own research on Google earth based on the markings and taxiway signs I could see presumably from the centreline.
So I wanna know why is the visibility 0000 when I could still see 46ish meters though vaguely but I could see it ?
Also,Does dos horizontal visibility effect the Low visibility procedures ? I mean if RVR is above CAT I conditions however the rest of airport has 100 meter visibility then would it still be Low Visibility procedures or just normal operations ?
Thanks

Related: What is the difference between RVR and visibility?

Does this answer your question? What is the difference between RVR and visibility?

Yes to an extent but I'm still wondering does Visibility affect Low Visibility procedures or not.


text:
What ILS type approach my flights landing could be?
I had one of the foggiest landing experiences recently and I'm interested if any of you could guess what type of ILS could it be like CAT I,II,IIIA or IIIB?
So the METAR issued 9 minutes before my flights touchdown stated RVR as 100 meters and the METAR issued 21 minutes after the landing stated RVR 750 meters.
The aircraft type is A321NX IndiGo Airlines and Airport VILK the RWY is 27.
Here are the METAR and TAF reports ..it could be wrong but I have just tried to gather them with the information I had so I'd love If someone could decipher it for me please !
METAR REPORTS
(After Landing and Deboarding)
SA 02/02/2021 03 : 30
METAR VILK 020330Z 00000KT 0100 R27/0750 FG NSC 11/08 Q1020
BECMG 0150 FG=
(During Approach and Landing) [Touchdown at 03:09]
SA 02/02/2021 03 : 00
METAR VILK 020300Z 00000KT 0000 R27/0100 FG VV/// 08/07 Q1019
NOSIG=
(During Holding Pattern)
SA 02/02/2021 02 : 30
METAR VILK 020230Z 00000KT 0000 R27/0075 FG VV/// 08/06 Q1019
NOSIG=
Below are the TAF reports for the flight -:
TAF VILK 020200Z 0203/0212 VRB02KT 0050 FG VV///
BECMG 0204/0206 0800 MIFG FG NSC BECMG 0207/0209 32004KT 2000 HZ=
TAF VILK 012300Z 0200/0209 00000KT 0200 FG VV///
BECMG 0204/0206 0800 MIFG FG NSC BECMG 0207/0209 32004KT 2000 HZ=

Welcome to aviation.SE! FYI, posting and self-deleting questions with no reason will risk triggering the automated anti-abuse scripts. The best course of action for the future is to edit your posts if you feel that you need to improve them.

The aircraft type is A321NX IndiGo Airlines and Airport VILK the RWY is 27...I don't know how to properly read METAR and TAF as I'm a beginner and I have learnt how to read a little from websites and but I'd be grateful if I could be helped with this query

The 3 METARs all indicate extremely poor visibility. The first one (02:30Z) said:

0000 R27/0075 FG VV///

which means visibility less than 50m (0000), Rwy 27 RVR 75m (R27/0075), fog (FG) and vertical visibility not measured (VV///).
The second METAR (03:00Z) still reports visibility less than 50m, but RVR has improved to 100m. The Airbus A321 is certified for CatIIIB down to RVR of 75m (Airbus getting to grips with CAT II / CAT III operations), so technically an approach would have been allowed before, but note that the METAR is only updated every 30 minutes. The pilots were probably informed by the tower or approach controller about the actual current RVR value.
After landing, the third METAR (03:30Z) already shows improved visibility of 100m and an RVR of 750m, indicating that the fog has started to clear.

Here are the minima for the Cat II/III ILS Rwy 27 approach at VILK (Lucknow):

The Cat II is out of the question with a required RVR of 300m (or 350m without autoland in Cat D aircraft). The Cat IIIA would have required at least 175m RVR.
Since the RVR was reported as 100m before landing, the pilots must have prepared for a Cat IIIB ILS approach with autoland. Once the pilots verified that the requirements for a Cat IIIB approach are fulfilled, it does not really matter if the RVR gets a bit better by the time they land, so even if it was 200m at the time of landing, the approach would have been performed with Cat IIIB.

Landings with Cat IIIB seem to be quite common in India according to bangaloreaviation.com:

On the domestic side, only the A320 operators Air India (NACIL-I), GoAir, IndiGo, and Kingfisher have most of their pilots Cat-IIIB certified. Boeing 737 operators Jet Airways, JetLite, and SpiceJet have their pilots certified to the lower Cat-IIIA standard (175 metres runway visibility).
[...] not surprising since the Airbus A320/A319/A321 comes with Cat-IIIB capability built-in, [...]

I have found the METARs and TAF also of that day..I would love to understand it better from you..should I post it here ?

Yes, you can edit your question to include them.

Ok thank you sir..can I direct message you here...because I'm new on this website So I don't know much ..I hope you understand..plz forgive if I make any mistakes.

No, everything is public here so others can learn from it as well. You can have a look at the tour to see how the site works.

I have edited and added the metars of before landing and after landing and also TAF as I was able to gather from a website !..thanks very much for your help !

I think here it won't get posted here but I have mentioned in the question itself...I always wondered it and have been super excited to know about it because I always wanted to experience a CATIIIB ever since my airport got it back in 2016 and to know that I really experienced it ..is the best feeling ever !!

Thanks for your answer Mr Bianfable ..So It means My Landing indeed was a CAT IIIB landing right ?

As I said, we don't know the actual RVR at the exact moment of landing, but the approach was indeed performed under Cat IIIB.

Thanks a lot Sir...I actually have gotten a video of it too and it even the sharklets of the a321Neo are hard to see in it even after the plane is on the runway and also taxing was super slow..we went all the way to the end of the runway and backtracked and then exited via taxiway C...It was the first time I have ever seen such a scenario... but it was magical .oh BTW it must be automatic landing right ?

Makes sense, the airport Low Visibility Procedures (LVP) say: "ACFT shall exit and enter RWY via TWY C"

Just one more thing..I have read CATIIIB landings are Automatic landings so It must be an autolanding right ? Also we parked at parking bay number 13 ..I recorded all the meticulous details so I could remember this experience forever !

Yes, it was for sure an autoland. Even Cat IIIA landings are always autoland, except with an approved HGS (Headup and Guidance System).

Thanks a lot Sir...I can't express how thankful I am of you...Over a month I was looking for answers and I tried decoding metars and everything online but Finally...I have the answers and Its a great feeling to know that I experienced an autoland..Thanks again Sir

Oh also I have a few more questions...would it be ok if I ask more related to this experience ? Also I'm really sorry if my questions are really senseless..I'm just curious about something that I experienced for the first time and I'm excited to know more about it.

This comment section is already very long and will probably be deleted soon by a moderator. If you have a new question, you should better ask it by pressing the Ask Question button at the top of the page. You can link to this question, if it is relevant for context.

Let us continue this discussion in chat.


text:
What are typical control surface deflection "rate" limits for transport airplanes?
I was wondering if anyone knows what are some typical control surface/actuator deflection "rate" limits for transport airplanes (i.e. aileron/elevator/rudder deflection rates)? I haven't found any useful information about the deflection rates yet.
Also, are there any ATR-42 500 manuals/references that give control surface deflection limits?
Thanks.

Welcome to aviation.SE! We have a couple of questions on this already: here, here. Do either of them help?

@Pondlife, thank you! The links you provided are related to my question, however, I wish the first link would provide any references in regards to the answers.. I am building an aircraft simulation of a transport aircraft (ATR 42) and was trying to set some control surface rate limits... or at least have a ball park from a reference of what those limits could be but haven't found any good reference yet.

I know flight control systems of the CRJs intimately and I'm not aware of any specifications on the "speed" of surface movement and there is certainly no testing requirement to measure movement rates, only deflection limits.Rates depend on hydraulic power available to push against air loads in response to a rapid control input.With minimal loads, the surface will move as fast as you can move the stick. With high airloads there eventually gets to be a bit of a delay or lag but I've never seen a spec.On CRJ200 there is no rudder limiter req'd because  PCUs can't make full travel at high speed.


text:
How common were (are?) hydraulically driven fuel pumps?
The XB-70 had a large number of fuel transfer pumps (something like 25) to transfer fuel from the 10 other tanks into the sump tank, and then three fuel "boost" pumps to pump it from that to the engines. These were hydraulically driven pumps. I.e. it was the hydraulic pressure in the corresponding hydraulic system that caused such a fuel pump to do its work. How common was that back in the days? Do such pumps exist on any current aircraft?

Not common, no:

The pumps mentioned in OP are fuel transfer pumps, necessary for the shift of Mean Aerodynamic Centre in supersonic flight. Subsonic aeroplanes do not require fuel transfer in longitudinal direction.1

A hydraulically driven fuel pump is subject to failures in the pump itself, plus failures in the hydraulic system driving it: leaks, dirty filters, burst pipes etc. Meaning an exponential increase in chance of failure of the hydraulically driven fuel pump.

So no, hydraulically driven fuel transfer pumps are not common. By way of comparison: the B737 has fuel pumps that are mechanically driven by the engines, plus AC driven electric pumps and gravity transfer to the centre tank as a backup option.
1 The A380 has a fuel trim tank in the horizontal stabiliser, if the transfer pumps fail fuel can be transferred back into the main tank via gravity.

The usage of horizontal stabiliser fuel trim tank dates is a classical on Airbus long-range models, at is was present on Airbus A330/A340. Such a tank is also present on at least on Boeing 747-400

(Also the fuel boost pumps in the XB-70, that pumped fuel from the "sump" tank to the engines, were hydraulically driven, although the snippet in my screenshot doesn't mention those.)

I suspect that even with the fuel trim tank inoperable in any way (full/empty), the stabiliser of an ordinary airliner is more than strong enough to compensate and keep the aircraft trimmed. Deltas like the XB-70 or the Concorde have no such redundancy.

@Tootea It's the shift in MAC that necessitates pumping fuel around in supersonic aeroplanes, not possible to trim it away, the CoG needs to shift accordingly.

The first Airbus with a trim tank was the A310. It then went on the A300-600 and as mentioned the A330/A340. The A350 does not. The MD-11 also has a trim tank.


text:
When was TACAN (or DME?) Y mode introduced?
If I understand correctly, originally DME and the equivalent distance measurement aspect of TACAN had only the "X" channels where the pulse pairs are 12 μs apart, and later the "Y" channels were introduced (to TACAN only?) with 30 μs separation. When did this happen, in the late 60s/70s era? So airborne TACAN equipment from before that would not have any X/Y selection possibility, right? Picture of the TACAN panel in the XB-70, which doesn't seem to have any X/Y switch as I see in newer aircraft.

Civil DME and TACAN share the same frequencies and the same 252 channels.
TACAN is standardized in MIL-STD-291.

1956: MIL-STD-291
1958: MIL-STD-291A
1967: MIL-STD-291B
1998: MIL-STD-291C

1958
I have not been able to find the two first versions, and cannot know directly whether these channels existed in 1958, but some documentation is available from NATO archives, e.g. in this description dated May 1959 only 126 channels are mentioned.
TACAN panel from this era, for ARN21:

ARN21 control panel, source
1967
MIL-STD-291B from 1967 mentions 126 X channels and 126 Y channels, and also that 126 channels taken from X and Y modes are allocated for Air/Air communication.
So the change occurred between 1959 and 1967.
In the meantime
Looking at NATO archives it appears a problem with the number of channels in Europe arose around 1964. A study was conducted.
The decision to double the number of channels was taken after this study, in March 1967:

The new standard with 252 channels was published in December 1967.


text:
What legacy turbojet would have detailed documentation and drawings available for free or cheap?
I am fascinated by the technology of jet engines. As a hobby, I might like to create a detailed animated 3D model of one (and publish it with a Creative Commons license). Obviously I am not going to find any actual detailed technical drawings of recent or current in-production engines. They are trade secrets or even military secrets. But models from the 50s or early 60s might be a different story. Looking for suggestions for a model for which ample documentation is available, for free or for a reasonable price. It is not important as such whether it is a British, American, or French or other continental European design.
(I am at the moment building an add-on for Microsoft Flight Simulator of the English Electric Lightning that uses the Rolls-Royce Avon Mk 302, and have not been able to find any detailed information about that late Avon model. Some documentation for earlier Avon models yes, but not very detailed drawings. So the Avon is not the answer. Anyway, for that purpose I don't need to model the engine in great detail. It would just be nice to at least get the dimensions and number of compressor and turbine blades and stator vanes correct, if I bother modelling those.)
Perhaps even some Soviet one (with ideas "borrowed" from a Western model)? One might imagine that when the USSR collapsed, lots of military-related technical manuals and drawings ended up for sale to enthusiasts. I don't know Russian but drawings with measurements would be useful anyway.

For the level of details and accuracy you're seeking, it is possible to use publicly available documents and obtain something credible enough for animation, even for modern turbo-engines. You can start from a general drawing, and then look for parts at vendors, or maintenance pictures. Be aware using Blender for CAD drawings is a nightmare, but feasible.

Many data can be retrieved from this video (this is still the same engine)

@mins Aren't the LP compressor fan blades oriented the wrong way in that video? As in that video, they would push the air the wrong direction, no? Compare to the fan blades. The HP compressor blades are the right way.

You're right, the fan blades are correctly shown, the LPC blades are wrong, as well as the stator vanes! Correct orientation  - source. A view of similar LPC blades.


text:
Early "digital" rotating digit wheel type gauges
The XB-70 has a "digital" gauge showing the total fuel quantity using six rotating digit wheels (as in mechanical counters, odometers etc), and another showing the fuel quantity in the tank selected (out of 11 tanks) by a knob.

I wonder, surely these indicators did not work like mechanical odometer-style counters so that when going from displaying quantity, say 56432, to another, say 45123, the units wheel would be spinning like crazy, the tens wheel would be spinning at one tenth the speed of that, the hundreds wheel one tenth of that, etc?
But instead, I assume each digit wheel was individually electromechanical driven, and the they all just moved simultaneously to the new positions showing the relevant quantity.
Or was the total amount displayed perhaps rounded to the closest thousands anyway so that the four rightmost digits were actually coupled, and the selected tank quantity rounded to hundreds, so that the three rightmost digits were coupled? The position of the digit wheels in the picture do seem to suggest that. But then one wonders what the point in having such a "digital" display was, if it is rounded so much that some round gauge with a rotating pointer would have given the same accuracy anyway.
Anybody have any definite knowledge, or an educated guess? Hmm, I probably should search on patents.google.com, things like these were surely patented.

It looks to me as though there are four wheels: three for the leftmost three digits, and one wheel that can display ten different things: "000", "100", "200", ... , "900".  So the two rightmost digits displayed are always "00", and the display has four digits of precision.  That is more accurate than a round gauge would be.

Thanks @manassehkatz-Moving2Codidact, corrected it.

If I understand correctly, this question is really about how the lower "LBS SEL TANK" gauge changes if one were to go from the selected "6L" and quickly rotate the knob to, for example, "4" (number made up, don't know if it's "4" or "4L" and "4R").

@FreeMan Yes, that is correct. (Because the "TOTAL LBS" gauge hardly changes very rapidly.) (And yes, there is a tank "4". Thew wing tanks are 6 to 8, L and R.)

It depended on the indicator and what it was trying to measure. The encoding altimeters on some earlier Boeing jets had a similar style readout that had the two rightmost digits linked and displayed in increments of 20 ft but the rest of the digits were independent. Meanwhile the EAS-Knots, Digit Altitude and Digit Mach Number mechanical readouts on the SR-71 were single digit precision readouts.

But then one wonders what the point in having such a "digital" display
was, if it is rounded so much that some round gauge with a rotating
pointer would have given the same accuracy anyway.

If the range of measurement is sufficient, even with rounding the digit style display can provide more information than a round gauge style readout, in some cases they also provide more direct information that prevents the pilot from needing to interpret multiple arms to derive a single measurement (e.g. digital clocks vs an old 3 hand clock).

when going from displaying quantity, say 56432, to another, say 45123,
the units wheel would be spinning like crazy, the tens wheel would be
spinning at one tenth the speed of that, the hundreds wheel one tenth
of that, etc?

Many aircraft instruments of the "steam gauge" era do not provide instant results. The common vertical speed indicator has a quoted 6 to 9 seconds of lag before the measurement should be considered accurate so depending on how these gauges are fed they will change readings as fast as they can and that was largely considered acceptable. Again, if they are individually driven that would be dependent on design and implementation.

A bit of a side note but important to the question, fuel burn schedules in aircraft are typically prescribed before hand, very specific and very well planned in reality fuel gauges are used for lose reference inflight and flow meters + timing + good engine information is whats used to calculate fuel burn, these gauges would have been used to loosely confirm numbers inflight and not necessarily constantly flopped around.


text:
Anybody recognise the model of ADI on the XB-70?
Is this a model that was used on other aircrafts of the era, too? Looking for technical information about it and knowing the manufacturer and model number would make that easier.
The Interim Flight Manual says that "the sphere, receiving information from the auxiliary gyro platform system, is free to rotate 360 degrees about all axes". So it is truly a complete sphere? In what situations would it rotate significantly around the "polar" axis and show its "west", "east" or even "back" side? As can be seen in this image, the lower and upper regions of the sphere have compass directions. Are those parts rotating independently from the middle region, to show heading? There is a small gap that seems to indicate that possibility.

Edit: I now notice that the Interim Flight Manual describes a different kind of ADI than what the aircraft in the museum has. It looks quite different in this figure:

This kind of ADI probably indeed had a fully rotating complete sphere. At some stage that was apparently exchanged with the model that the first photo shows. In that I guess only the separate top and bottom segments (with the heading directions) are complete and rotate 360 degrees to show headings.

(This is from the USAF museum's fabulous 360 degree (the nerd in me wants to write 4π steradians) cockpit photo at http://www.nmusafvirtualtour.com/cockpits/RD_tour/RD-9.html ). The gyro compass below the ADI also shows the same 210 degrees heading, so that does indeed seem to have been the heading when the aircraft's systems were shut down the final time.)

The Mirage III had this kind of spherical indicator, combining attitude and heading indicators, known as Bezu ball, after its inventor:

Source.

So it is truly a complete sphere?

Yes.

Source.

In what situations would it rotate significantly around the "polar" axis and show its "west", "east" or even "back" side?

The instrument combines an attitude indicator and a heading indicator. The AI changes the up/down axis orientation, then this axis rotates to indicate the heading.

Source. This one was manufactured in 1957.
I believe it was customized by SFIM, a French company developing instruments under a Sperry license, for Dassault and not used by other manufacturers.
The ball was reused for Mirage IV and 2000, integrating more indications. Manufactured by SFENA and SFIM and known as synthesizer Chombard, still after its inventor. SFIM merged witin Safran in 2005.


text:
What is the definition of Taxiway Incursion?
I can't find any ICAO document that defines a Taxiway Incursion, but I can find some online presentations which were presented at ICAO workshops or seminars that loosely refer to Runway/Taxiway Incursions!
Runway Incursion is well defined and there is no doubt about its meaning or significance, but the question is: is every wrong turn during taxiing considered a taxiway incursion? If so, according to what official definition?
ICAO Annual Safety Report Group

I haven't seen it explicitly defined, but the meaning can be inferred by comparison to the definition of a runway incursion. ICAO defines a runway incursion as "any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft." Thus a taxiway incursion would be "any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on a taxiway.
There doesn't need to be an official definition to use it in a presentation. If you say "Runway/Taxiway incursion," everyone who knows what a runway incursion is can pretty much guess what you mean by a taxiway incursion.
A wrong turn while taxiing is only a runway incursion if it takes you across the hold short line for a runway. Presumably it's a taxiway incursion if it takes you onto a taxiway that you are not supposed to be on.


text:
Is this a normal flight path to take?
A few days ago I was flying from Munich to Chicago, the flight arrived about 20-25 minutes late, at some point, the pilot suddenly turned in completely the opposite direction as we were approaching Chicago, they then circled around, I was able to take this video (uploaded as a .gif)
https://i.sstatic.net/KUPRN.jpg
I had to miss my next flight due to the delayed arrival and the flight they then scheduled me on was delayed twice in that day. Now I'm asking out of curiosity about what would have caused the pilot to take such flight path.
As for flight details,
Flight No: Lufthansa 953
and Flight Time: July 7th, 11:55 am from Munich, Germany (MUC-Franz Josef Strauss Intl.) to Chicago, IL, United States (ORD-O'Hare
Intl.)

LH 953 is from Birmingham, UK to Frankfurt. Do you mean UA953, which is the code sharing Lufthansa flight?

@GdD This is what my itinerary has, I do believe that it is indeed UA953 on the United app.

ORD was busy & backed up pretty heavily on July 7 (I was there that day.) Plenty of inbound flights were holding, which is exactly what seems to be going on in that video. Not surprising that things ran late; too bad the connecting flight didn't run similarly late.

Yup. They did one racetrack pattern but the second was cut short into a 360.


text:
Change of absolute ceiling with weight
Let's say an aircraft has an abs ceiling of some value at the start of its cruise and then it consumes some percentage of its fuel during cruise. How will this change the new abs ceiling at the end of its cruise? Is there any mathematical way of finding the new abs ceiling?
For example: At the start of its cruise a jet aircraft has an absolute ceiling of 35 000 ft. During the cruise it consumes fuel equal to 20% of the aircraft’s starting weight, what will the aircraft’s
absolute ceiling at the end of the cruise segment be?

It might be helpful to mention a specific aircraft, as Mach and the ability to generate thrust at a higher altitude will be important along with weight.

The question is applicable for any given commercial airliner. I thought the info provided in the question was enough to find the new abs ceiling. I'm just not sure about the maths behind finding it

Probably Mach limited, and with an airliner, a max safety altitude.  My guess is, from a thrust point of view, airliners do not come anywhere near their absolute (or service) ceiling.  So, it becomes a matter of "how much does my weight savings allow me to slow down (indicated) at my Mach limit (TAS) without wasting fuel (maintaining optimal AoA).  Climbing allows you to fly at a lower IAS for the same TAS, but lift is proportional to V$^2$.  Within your Mach limit, your allowable  IAS reduction will be $square root$ weight reduction.

Cheers. I'm trying to get a mathematical view of this scenario. Since less weight means greater altitude, I'm assuming at the end of its cruise it will be in the stratosphere. I'm also assuming weight is proportional to the density ratio (sigma, σ). From https://www.digitaldutch.com/atmoscalc/ , density at 35000 ft is 0.3796 giving me a sigma value of 0.3099. After 20% weight gone, sigma should decrease by 20% as well (0.2479). Interpolating from the ISA table, I get the new ceiling to be around 39880 ft. This method looks kind of broken nevertheless. Lmk if this sounds alright or not

yes, if your engines can produce adequate thrust for the matching IAS at a higher altitude and your Mach is ok.  Check your TAS.

Short answer: The new aerodynamic ceiling is 40,000 ft density altitude.

Constant Temperature Condition
It is instructive to imagine the following scenario: The aircraft is flying at the coffin corner at 35k feet (density altitude).
$L = W = ½ \cdot ρ \cdot V² \cdot C_lmax \cdot S$
The 'W' represents weight (in Newtons), which we are assuming to be equal to lift. In this case, the 'V' (TAS) is at it's maximum limit, which cannot be exceeded without having a shock stall (and a subsequent collapse in $C_l$). 'V' is also at it's minimum limit, which cannot be subceeded since that requires an increase in $C_l$, which is not possible since $C_l$ already equals $C_lmax$. It can be seen that any change in 'V' would ultimately result in a stall.
Now reduce the weight by 20% (W' = 0.8W), this means that the $C_l$ will be 80% $C_lmax$. If the aircraft is slowed down now, it won't stall, since there is a headroom available in $C_l$. This will also alter the shock stall speed (shock stall speed changes with $C_l$), but for the purposes of this question, it does not make any difference, and so we will assume that it doesn't change.
Now, we will start a climb at a constant Mach number - the same Mach number that we had earlier in the coffin corner. Doing so ensures that we never exceed the Mach number for shock stall (we're basically climbing alongside the buffet boundary). At some point in the climb, the aircraft will again attain the $C_lmax$ (stall boundary intersects buffet boundary), and will again find itself in the coffin corner - the altitude at which this happens is the new aerodynamic ceiling.
Since in the question we started at 35k feet, the aircraft was basically at tropopause, and so we can assume that the temperature is constant throughout the climb (how convenient is that!). This means that the Mach number of the aircraft varies ONLY with TAS - this also means that a climb at a constant Mach number is same as climb at a constant 'V' (TAS). And with that, this particular case is solved:
$W = ½ \cdot ρ \cdot V² \cdot C_lmax \cdot S$
removing all the constants from this equation (including 'V'), we get the following relationship:
$W ∝ ρ$
And so reducing the weight by 20% reduces the minimum necessary density $(ρ)$ by 20%. Which altitude has 20% less density than that at 35k feet? According to ISA charts, that altitude is 40k feet.

ISA Chart

Variable Temperature Condition
In the previous case, we conveniently assumed that the temperature was constant, and so a climb at constant Mach number was the same as that at a constant TAS. This is not always true, so let's look at a more general case.
Consider the same previous case of climb at constant Mach number, except that 'V' is no longer constant; as the altitude is increasing, the temperature and thus the speed of sound (a) are decreasing. For a constant Mach number, a reduction in 'a' requires a reduction in 'V'. From the previous equation, if we again remove all the constants, we get:
$W ∝ ρ \cdot V²$
'V' was not removed this time since it is no longer a constant - it's a variable, the value of which is not obvious (again, V is reducing as altitude is increasing). However, it is possible to substitute it with something known... We are climbing at a constant Mach number. What is Mach number?
Mach number $(M) = V / a$
$or, V = M \cdot a$
What is 'a' (speed of sound)?
$a = √(γ \cdot R \cdot T)$
This implies that:
$V = M \cdot √(γ \cdot R \cdot T)$
Again, removing all the "unnecessary" constants from this equation, we get the following relationship:
$V ∝ √T$
or $V² ∝ T$
Simply substituting this into the previous relation, we get:
$W ∝ ρ \cdot T$
Where 'T' is the absolute temperature (in Kelvin). Now as we can see, there are two variables to worry about: $ρ$ and T. But that's not a huge problem, since each altitude generally corresponds to a particular density and a particular temperature. By looking up these two values in the chart, the new aerodynamic ceiling can be determined for a given change in weight.


text:
Where is the V3 airway mentioned on the ILS 34 approach plate for KPSM?
While drafting a simple flight plan for KBOS to KPSM, I noticed that the ILS 34 Approach plate for KPSM mentioned that the procedure turn is "NA for arrivals at PSM VOR/DME on V3 northbound":

What does "V3" mean in this context?  I assume it's a victor airway, but I don't see a V3 on the VFR map:

V3 doesn't seem to be a radial from the PSM VOR, since neither 003 or 030 radials intercept the approach course of 345.

Welcome to aviation.SE! We usually prefer to have each question asked separately, so you might want to ask your second question about filing in a new question.

Sure. Edited to remove 2nd question.  The answer to the 1st will imply an answer to the 2nd.

V3 does indeed refer to the low-altitude Federal airway designated "V3" which is defined in the 7400.11E (page E-1028) as:

From Key West, FL; [many other VORs and intersections]; Boston; INT Boston 014° and Pease, NH, 185° radials; Pease; INT Pease 004° and Augusta, ME, 233° radials; Augusta; [several other VORs and intersections]; Presque Isle, ME; to Quebec, PQ, Canada. The airspace within R-2916, R-2934, R-2935, and within Canada is excluded.

But on the current version of the charts (as @mins says, you should look at the Low Enroute chart, not the VFR chart) V3 seems to end at BOS and does not appear again until PQI. From PQI, V3 exists westbound direct to YQB until intersecting the Canadian border (where it terminates at a point named LABRE). So what gives?
Look again at the document control page for the 7400.11E and click on the "Amendments" link. It becomes apparent that a change numbered 20-AEA-10 went into effect in April 2021 amending, among other airways, V3. The airway definition now reads:

[yadda yadda yadda]; to Boston. From Presque Isle, ME; to Quebec, PQ, Canada. The airspace within R-2916, R-2934, R-2935, and within Canada is excluded.

So the ILS Runway 34 approach plate references an airway that no longer exists at that location. Perhaps you should bring this to the attention of the charts and procedures office by submitting an Aeronautical Inquiry.

Thanks! I was wondering where the airways were defined. I did wind up submitting an inquiry as per your suggestion and will update with their response here.

FAA replied: "The note can be disregarded and will be removed on a future amendment."  I assume they mean they are going to rollback 20-AEA-10 and V3 will be re-introduced around KPSM.

@Chris I would very much doubt that... more likely they will do just what they say, remove the note and leave it at that. (I'm not sure if those "Procedure NA" notes are there because of the sharp turn required or to prevent traffic conflicts.)


text:
Can "Center" provide VFR flight following?
Whenever I've requested VFR flight following, I've always requested it from So Cal Approach/Departure because I'm usually flying within their reach.  If I'm flying outside the reach of So Cal Approach (out in the desert), can I contact Los Angeles Center for VFR flight following?  If I do this, the frequency for contacting Los Angeles Center doesn't seem to appear on the VFR charts, but is shown on IFR low charts.
Also, does the radar coverage of the various "Centers" cover all of the continental US, or are there remote areas where Center's radar and radio communication can't reach?

Any US radar facility can (and will, workload and coverage permitting) provide VFR Flight Following, whether Approach/Departure or Center.
Look up the airport you are departing or, if already airborne, the nearest airport in your general direction of flight in your A/FD, EFB or (if you’re lucky) glass panel. The App/Dep lines will give you the frequency and name of the facility to call in that area.
The coverage problem is mostly an issue of altitude rather than range. Center radar and radio sites are further apart, so due to terrain and the curvature of the Earth, they may not be able to see/hear you if you’re too low. Typically 3,000 AGL is high enough, but if not, just keep climbing and try again in a few minutes.

Centers regularly provide flight following for VFR aircraft, as an additional service. It's a bit different from Terminal flight following, however.
You can contact us using the low IFR chart frequency, or look up an approach plate near where you are flying for a frequency.
We will normally want your aircraft ID, type, equipment qualifier, and destination, so we can enter a flight plan. If you are doing a round robin, a photo mission, or a sightseeing flight, it's handy for us to have a general idea of your intentions, which we use for briefings, and, if necessary, search and rescue.
We will provide traffic advisories and alerts, advise you of any special use airspace, TFRs, etc, that you may encounter, and can provide information regarding radar displayed weather, etc.
We can vector you around such items, upon pilot request. We usually only initiate vectors for TFRs or traffic. If you want a vector around an SUA or weather, let us know. If a vector will put you into IFR conditions, you'll also need to let us know.
Centers, however, may not be able to provide services if you are below radar/ADSB coverage, or out of frequency range. Also, we can terminate the service at any time. (We usually don't, unless it's radar, frequency, or workload related)

I have never called up Center for Flight Following, but I have certainly been passed to Center for Flight Following.  I would imagine if they "accept" you from a Departure controller, then they would accept you from a radio call.  That being said, like all things related to Flight Following, it is controller workload permitted.

To answer you first question, yes you can call center. I have heard of people doing that before. However center is generally for IFR aircraft so it may not always be the best idea. I also checked the Pilot/Controller Glossary and it backs that up. It says "AIR ROUTE TRAFFIC CONTROL CENTER− A facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/as- sistance services may be provided to VFR aircraft.
(See EN ROUTE AIR TRAFFIC CONTROL SERVICES.)
(Refer to AIM.)"

VFR flight following is considered an "Additional Service in an ARTCC. These services are provided on a workload basis. The controller is obligated to provide them if workload permits. This means that if the controller CAN provide the service, they SHALL provide the service.


text:
What button do I push on the instrument panel to activate DME in VOR navigation?
For some strange reason I cannot seem to find any information about what button to push on the instrument panel to active the DME.  There is plenty of information about how DME works with interrogation and slant distance, but I cannot seem to locate any information about what button to actually push to activate DME when I am sitting in the cockpit (in a Cessna 172, for example) or where to look on the instrument panel to read the measured distance the DME is telling me.  So if the DME is measuring 8 nautical miles, where on the instrument panel will that "8" be displayed?

If I asked you "what button do I press in my car to turn on the air conditioning?", could you tell me? Without any information about the car model or interior? Even the same model of aircraft can have completely different avionics and instruments. To get an answer, you need to tell us what aircraft you have and exactly which instruments you have in your cockpit. For example, do you have an integrated glass panel like the G1000? Or traditional 'steam gauges'? Or something else? If you don't know how to identify the instruments, a picture would be very useful.

I'm voting to close as there's not enough information to answer. Is DME even equipped on the airplane? In many training organizations airplanes have very different instrument fits, there's no way to guess reliably.

Wow, tough crowd.  My question was answered adequately by Jamiec.

Typically, there isn't a "button" as such, you tune the DME to the frequency of the ground station (or slave it to the NAV radio).

The knob on the right is used to tune a frequency (shown before MHZ) when in "frq" mode, which is usually a VOR/DME. The numbers before NM is your distance to/from the station in Nautical Miles.

This answer makes sense to me.  None of the steam-gauge Cessna airplanes I have flown have had a separate module for DME, which explains why I was confused about which button to press to activate it.

For the classic DME instrument, see Jamiec's answer.
If your aircraft is equipped with a G1000 glass cockpit, the DME window needs to be enabled via the PFD menu using the buttons at the bottom of the PFD:

Displaying the DME Information Window:

Press the PFD Softkey.
Press the DME Softkey to display the DME Information Window.
To remove the DME Information Window, press the DME Softkey again.

The Window will then be shown to the left of the HSI at the bottom of the PFD:

DME INFORMATION WINDOW
The DME Information Window is displayed above the BRG1 Information Window on the 360° HSI and in a box above and along side the Arc HSI. It shows the DME label, tuning mode (NAV1, NAV2, or HOLD), frequency and distance. When a signal is invalid, the distance is replaced by -.-- NM. Refer to the Audio Panel and CNS Section for information on tuning the DME.

Source: Garmin G1000 Manual - Cessna Nav III

Haha yeah. Number of times I've seen a G1000 in a C172 - once. X-Plane :D

@Jamiec All new C172s have the G1000, but I bet more than 90% of the world's C172s are still using steam gauges ;)

Indeed, every C172 i've flown is pre-1990

@Jamiec - Yes, G1000 availability is highly dependent on the model. I’ve never seen a C172S or SP in real life without a G1000. Then again, I’ve never seen a C172E, G, L, M, or N with a G1000. Although, I have seen the older models retrofitted with Aspen and Dynon systems.

@Jamiec: Heck, every airplane I've flown is pre-1975.

Both Jamiec’s and Bianfable’s answers are right for the avionics equipment represented in their posts. Your actual answer will depend on what equipment you have in your aircraft. In my own recent experience, I have not seen an operable DME radio in a Cessna 172. I’ve only seen one operable ADF in a Cessna 172. In most cases, they will look like smaller versions of your NavCom radio. Mainly, I see at least one of the NavCom radios retrofitted to a GPS unit like the Garmin G430 or G530. This is a preferable expense than maintaining technology that is becoming increasingly obsolete. And, per AIM 1-2-3, RNAV/GPS can be substituted for DME.
If you are flying a glass panel aircraft like one equipped with a G1000, G500, or Dynon Skyview, the GPS distance to your selected point will be displayed on your PFD and is an option on your MFD. This can be found in the top info bar of your PFD. As long as the position of the NavAid is updated in your GPS database, you can select it as a fix and use this distance for navigational purposes.


text:
How are ejection seats tested?
How does a company like Martin Baker, evaluate the safety of their ejection seats. Are there any standard metrics or tests that exist? If not, what would be the suggested tests to be performed before they release the seat.
Edit: I am more interested in the type of data they collect from the tests. If I were to create a ejection seat on my own, what quantities would I use it to compare it against Martin Baker's seat?

It's actually pretty common to modify a twin seat fighter to test the seat. The rear seat ejects the test unit with dummy weight while the pilot flies the airplane in the front seat.

I remember reading that Martin Baker in particular build their seats in batches of 105, and then test-fire 5 of them. If any of the five fail the whole batch is scrapped. That was a while ago and I can't find a reference. I'll make this an answer if I find one.

Martin-Baker tests their seats in an actual aircraft. They have, for some time now, used a Gloster Meteor to test their designs as discussed in this question. They also have a high speed sled at their facility for such tests.. 0-0 tests are easier to pull off since there is no moving component.
Individual components like explosive bolts or handles are likely tested like any other engineering component, in a test facility.

@MichaelHarvey I have updated to reflect, thank you.

EJECTION SEAT TESTING
  An intrepid employee, Bernard Lynch, attempted the first static ejection on 24th January 1945. He then conducted the first mid-flight test ejection on 24th July 1946. He ejected himself from the rear cockpit of a specially modified Meteor 3 at 320 mph, 8000 ft in the air. Bernard Lynch made a perfect landing and subsequently made a further 30 ejections.

But now they use dummies with sensors.

See this video and also this one
Source:

http://martin-baker.com/about/history-founders/
http://martin-baker.com/services/testing-and-qualifications/


text:
Why are some A350s missing SSA probes on their nose?
I recently just noticed that some A350s are missing their iconic set of 3 main SSAs (Side Slip Angle Probes) on their nose. I'm not sure if its an issue of newer variants or varied airline options, but I'm sure it has something to do with a less needed sense of redundancy. Any exact answers behind this?
Thanks!
Picture sources:
Top:https://www.traveller.com.au/the-inside-story-of-the-a350-airbus-rival-to-the-boeing-787-dreamliner-12c17x
Bottom: https://airwaysmag.com/airlines/british-airways-takes-off-a350-1000/

From a Google search for A350 images it seems that the pitot tubes you say are 'missing' are only found on Airbus' own aircraft. That suggests that they're associated with some test systems not installed on production aircraft.

@CatchAsCatchCan I have seen most, if not all A350s that have entered service with airlines with these 3 pitot tubes though... I'm just not sure why some, in particular, don't have them.

@quietflyer definitely a good suggestion, just edited the question

You are right: the three side slip angle probes are redundant because side slip can be calculated by the ADIRS without these probes. Airbus included them in earlier A350 models to crosscheck this calculation, but they are removed now:

Spot the difference 2: SSA (Side Slip Angle) Probes.

This one’s a bit more technical. If you look closely around the nose of the aircraft, you can see an array of sensors. These form part of the Air Data and Inertial Reference System – in other words, they feed flight parameters to the pilots, such as the angle the aircraft is flying, the outside temperature, and the barometric and static pressure.
As the A350 entered service, Airbus still wanted to gather more information to compare the data between different systems that help pilots fly on approach in crosswinds. To do that, a few early models had extra probes added to cross check the data from the other instruments. You can see these three extra vanes on the front of the aircraft just below the ‘Zorro’s Mask’ windscreens. Having now gathered enough side slip information to establish that they’re not required, they’re being removed on all new A350s. They’ll also be taken off our first two aircraft in the coming months, which will save weight and maintenance costs.

(Virgin Atlantic Blog: Airbus evolution: Can you spot the difference?, emphasis mine)

I sense another ASE question in the making here-- what is the advantage of a complicated pressure-sensing system to measure sideslip, as opposed to using the slip-skid ball or an equivalent inertial sensor?  Is it really during a crosswind approach and landing, that it makes a significant difference which system you are using?

@quietflyer I sense yet another ASE question: Why was Airbus unable to confirm the accuracy of the ADIRS during flight testing to a satisfactory degree that they needed to include the extra pitot tubes on production aircraft to continue the validation process?

@FreeMan The original post is a bit misleading, the early production aircraft would most likely not have kept the sensors to keep testing if they were needed.
The modification process takes months, if not years. By the time there was enough flight test data from the actual flight test aircraft to confirm that the sensors were not needed, there would have been multiple aircraft already in production. Then, once the data had been confirmed, the process to remove the sensors from the designed configuration could start, taking time (as mentioned). All this time the production of aircraft would have continued with the original design. The modification would have been made “retrofittable” thereby allowing aircraft already been delivered to be updated (through service bulletin). Hope this clears up your question, albeit a couple of years late.

This addresses a comment on a previous answer, rather than being an answer in its own right.


text:
How unusual is it for 3 or more E-6 planes to be airborne at the same time?
I noticed there are at least 3 x E-6 aircraft flying at present (call signs: MAYO38, NANA67, and one more which may have landed before I grabbed it), along with an E-4B.
These aircraft are said to house Military Generals and other important people during times of nuclear escalation.
Is it common for there to be 3 or more E-6 aircraft airborne at the same time?

I could tell you, but I'd have to kill you.

With 16 aircraft, I would expect you could easily have 2 in the air (2nd goes up before 1st comes down so that one is always literally in the air) and then a 3rd go up for training or for flight testing after maintenance, transfer to a new base or whatever.

Simpleflying reports that

The United States Navy has a fleet of 16 E-6s and has typically at least one of them in the air at all times. It is also not uncommon to see two or three in the air at the same time.

More materially, that report also quotes a 2020 Oct 2 tweet with diagrams showing that E-6A AE0414

was publicly tracked on 20 out of the past 31 days

and that E-6A EA0415

was publicly tracked on 18 out of the past 31 days.

That's not quite three at once, but if two of them are publicly trackable for more than half the days of a month, it's plausible that some of the other fourteen were also airborne then.


text:
Are more fatalities in commercial aircraft accidents caused by pilot error than by automated features?
This claim struck me:

Overall these automated features are an overall benefit to everybody. They are preventing some of the more classic aviation disasters that pilots can induce into these aircraft.

Question
Is it correct that pilot error causes more fatalities in commercial airline accidents than those caused by automated features, like MCAS?
The reasons it struck me are two-fold:

There have been very prominent accidents involving automated features in recent years
I don't know of many cases of pilot error causing commercial airline accidents (although I don't follow closely).

What I know so far
I ordered List of aircraft accidents and incidents resulting in at least 50 fatalities by date descending and examined the last 6 years' of crashes. It's easy to spot two caused by automated features: Ethiopian Airlines Flight 302, and Lion Air Flight 610, but I lack the knowledge to tell which others were caused by automated features, nor which were by pilot error. Note: I only chose 6 years because that's what fit on screen, a larger sample (perhaps 25 years) would be much more rigorous.

Hi Steve ,welcome to ASE. Your question is hard to answer, as one reason alone very seldom leads to an accident. Coincidentally, a model often used to investigate reasons leading to accidents is some times called "Reason model" by it's formal propounder James T. Reason (go figure...), more descriptive name is the "Swiss cheese model". Accidents generally are a instances where a hazard slips through a number of layers of defense, which for one reason or another are not functioning properly. Typical slices in aviation are the pilot, redundancy of the systems themselves, backup systems etc...

This may be somewhat unanswerable due to the prevention paradox: if automation was capable of mitigating all pilot errors, this would mean that all remaining accidents are due to failing automation.

One problem with this question is that accidents (not only in aviation) typically have multiple causes. Take, for example, the seemingly clear-cut automation issue with MCAS. Yes, the design of MCAS and the missing documentation were flawed; but there was also (1) Bad maintenance (sub-par replacement parts); (2) Insufficient pilot training (3) Pilot confusion and failure to react timely and correctly. This will likely be the case with most failures short of bombs and missiles.

How could anyone know that, but by asking the jurisdictional aviation authorities for accident records? Please be sure, those guys do keep records, with so much detail Jo Average would not believe…

Note that most "automated failures" are actually human errors because humans designed and manufactured the automated systems.  Of course, unlike the pilots, those humans aren't typically in the aircraft when they crash.

If you're interested in this topic, I'd recommend taking the time to watch the classic lecture about automation dependency Children of the Magenta Line (more about autopilots than newer systems like MCAS) by Captain Warren Vanderburgh of American Airlines in 1997. It's not really either pro nor anti-automation, but more of a really meaningful discussion about the importance of being able to select and use the right mode and level of automation for a situation and having the proficiency to drop down to lower levels of automation when necessary.

"Automation failure" tend to be lumped in with all other "Mechanical failure" in any statistics. Those statistics are fairly easy to find but absolutely back up the claim that pilot error causes far more accidents than mechanical failure
If we have a look at the data from the 2010s (which is the most recent in that link above, but has remained fairly consistent thoughout the decades)

Pilot error
Mechanical
Weather
Sabotage
Other

57%
21%
10%
8%
4%

So pilot error accidents causing fatalities accounted for more than the rest put together in the 2010's.

This begs the question of why have humans in charge if all the do is make mistakes! Which is a logical fallacy, what you can't see from the statistics is all the times the human up front made a decision which prevented an accident from occurring. It's still very difficult (if not impossible) to program a computer to make decisions in a rapidly changing/dynamic environment.

Those stats are interesting but difficult to rely on, as the database doesn’t show the cause for each accident. Also, there are often multiple causes in an accident. Take AF477 for instance. Is that an equipment failure (the pitot tubes froze and started giving incorrect information) or a pilot error (spatial disorientation and wrong reaction)? Also I counts accidents only, not fatalities.

Something to add to that last paragraph is that a lot of accidents where Human error was the cause, can also be traced back to a particular automated system malfunctioning, forcing the humans to do actions manually but are no longer used to. It's a paradox: more automation means less human involvement required, thus less pilots gaining experience manually flying the plane, thus when something does go wrong, they are less prepared to take over the task.
IIRC Fuerza Aérea Uruguaya 571 is an example of such an accident.

@jcaron: AF447 was definitely pilot error. The reason the pilots are there is precisely to deal with the situations in which the computer is not sure what to do, including the cases where an instrument fails. They had a perfectly functioning plane with a single sensor mulfunction; the pilot flying never understood what was happening, and the two others never completely overrode him, all three ignoring the majority of their instruments.

Which is why, @Opifex, driverless cars are so scary. When (not if) he automation fails, the already poor (American, at least) driver will be so far out of practice, he won't have a clue what to do.

Yes the flight crew is the key factor in the majority of crashes.  It's for this reason that two big innovations are largely responsible for the massive drop in fatal accident rates since the 90s (there hasn't been a crash of a heavy, loaded with passengers at least, in the US in over 20 years - think about it... 20 years, and that was a pilot-induced rudder-fin failure).
The first and biggest is Crew Resource Management theory, which started to be implemented in the West in the 80s.  CRM was so successful that its concepts have spread far and wide outside aviation, from policing to surgery.  The other one is Flight Management Systems and the two dimensional map navigation display made possible by the "glass cockpit" (also in the 80s).  It's hard to exaggerate how much 2D moving maps reduced crew workloads in terminal areas and on approaches, by reducing the dependence on a pilot's internal mental "map making" abilities to maintain situational awareness.
Fatal crashes caused by system failures are exceedingly rare, because at the certification level, system design requires a mathematical probability of better than one in a billion of a component failure leading to an airframe loss. MCAS can be discarded as a Black Swan event, a culmination of a set of very unique circumstances and decisions at the certification and development level (I mean, so unique that the project chief test pilot was charged criminally for hiding information from the FAA). MCAS can be thought of as "pilot error" induced by a bad configuration that slipped through the cracks you could say, but which some crews could have coped with.
Double and triple systems redundancy is required to maintain this less-than-one-in-a-billion probability of disaster.  It's not perfect, but it's the main reason airplanes don't fall out of the sky regularly when components fail (and things are breaking down on complex aircraft all the time as you can see in an airline's dispatch delay rate - those regular delays leaving the gate are usually because the plane arrived with something broken that has to be fixed on the spot).
"Automation" in itself?  Yes automation could probably be said to have prevented some disasters, but in the bigger scheme of things, not as much as something like CRM.  FADEC makes engine operation a little easier and more convenient for the crew, but it mostly drives costs down.  Fly-By-Wire and other system automation controls?  They help reduce crew workload overall, and maybe cover for sloppy flying from time to time, but they are also mostly cost reduction drivers (FBW eliminates a massive amount of hardware). On the C-Series/A220, the systems automation level is just about at the pinnacle of current development, and the main benefit (and selling point) is a huge reduction in maintenance man-hours, more than safety.

Wasn’t the point of FADEC to eliminate the Flight Engineer, which reduced both opex and human error?

there hasn't been a crash of a heavy in the US in over 20 years. Well, there's GTI 3591. That was a 767. But, once again, pilot error.

FADEC came about long after FE's were already being eliminated by the new gen of 2 crew heavies like the 767.  But to your point, yes pre-FADEC you had electronic engine control, basically computer trimming of fuel schedules, and computer controlled monitoring and sensing with EICAS synoptics presented directly to the front seaters, and and those allowed FEs to be eliminated. FADEC is mostly about weight saving - eliminating cable runs as with FBW - and the ability to run engines much closer to their margins with much tighter control over temperatures, stall/surge, improving efficiency, etc.

@TomMcW hadn't heard of that one. Thanks.  There was also a crash of a heavy in the Arctic, flown by First Air in the mid 2000s where it ran into a hill because the capt became obsessed with regaining LOC and the FO was too timid to stop what was happening, but that was in Canada. Are their any other US heavy crashes in that time frame?

Asiana 214 happened in the US, and that was less than 10 years ago. First loss of a 777, multiple fatalities.

Oh yeah that was the one where the crew couldn't handle eyeball approaches.  My memory sucks.

One thing this answer kind of points at implicitly is that there are forms of automation, largely outside of the crew's control, that are really more about the design of flight control systems, like FADEC, FBW modes, and MCAS, and other forms of automation that are more in the form of controllable workload management tools for the crew, like autopilots and FMS guidance. It's kind of like the difference in a car between systems like anti-lock brakes and traction control vs cruise control. Lumping both together as "automation" is potentially confusing as the crew interacts with them differently.

Definitely.  A lot of the automation of systems is simply the replacement of mechanical hardware with electronic hardware, followed by replacement of electronic hardware with software, although there are reductions in workload somewhat, as with FADEC, bleed/pressurization control etc. I would say none of those things has had anything like the impact of CRM in the big picture.  On moving maps, I did the CRJ type course with a fresh instrument rating on steam gauges, and although they are very easy to fly, were it not for the Navigation Display and FMS, I would have been hopelessly over my head.

I'd like to point out a difficulty in providing you with an answer:
We know well the accidents caused by pilot error and automated features. However, we cannot be sure of how many cases would have gone downhill if the automated features weren't there to assist the pilots. Sometimes the pilots may have understood it but the cases weren't logged, and other cases the features might have provided support in the background and "saved the day" stealthily. (I'll try to get some examples in the future).
Now, I am hardly in a position to answer this, as my only experience is youtube watching and a couple hours flight simulator. But the maturity of the aviation industry as a whole amazes me (nothing is perfect, but I've not really seen any better). Each automated feature was born to assist, and many times the reason for it was to prevent conditions of some accident to happen again. So, in general, I'd say the features help.
To interject some personal ipinion: MCAS was one of the rare black sheep, with multiple entities working in a bad way. But it is rare. I guess it is a small reflection of the aviation paradox: it's the safest transport method, but if an accident happens in the other end of the world, you will learn about it and it will create fear, while the (thousands?) people dying via eg car is nothing interesting so it's not in the news.

Also, after stevec's observation in the comments, the opposite is also true: we also cannot be sure of how many cases the pilots saved the day by disabling the automated features. In order to keep supporting my pro-feature point, I will argue that features that are consistently creating trouble will be noted as such by pilots and reviewed....hopefully.

Black sheep=black swan?


text:
What is the accepted ADS-B quality indicator value from EASA/FAA?
I'm doing research that has to do with the ADS-B quality indicators. With the ADS-B quality indicators I've received, I want to compare them with EASA's or FAA's requirements for each ADS-B Version (260, 260A, 260B) and see if they have been met.
I am having trouble finding the right document that tells me the minimum requirement. The quality indicators I've received are NIC, NACp, NACv, SIL, GVA, and SDA. At the end, I want to show the statistics of how many actually complies with the minimum requirements declared by EASA/FAA per ADS-B version.


text:
What is the broadcast rate of an ADS-B message?
From what I know, ADS-B (DF=17) message structure is 112 bits long. In terms of type of messages it transmits, there are aircraft identification, surface position, airborne position with baro altitude or GNSS height, airborne velocities, aircraft status, etc. However, assuming an aircraft is on final approach and it broadcasts the necessary information to ground stations then to ATC, what is its transmission rate in seconds? Is it really 1 second per message or does it differ from the type of messages? What factors affect the transmission rate? Thank you.

It depends on the Message Format TYPE Code and the aircraft state. In your example, being on final approach would have no effect as the primary state criteria is being airborne (vs. surface). The rates are 'nominal' rates in that there is a programmed 'dither' to the nominal rate to avoid synchronous garble.
The nominal rate for TYPE codes 1 through 4 (ID and Type) is 5.0 sec airborne and 10.0 sec surface.
TYPE Codes 5 through 8 (Surface Position) rate is 0.5 sec in motion and 5.0 sec when stationary.
TYPE Codes 9 through 18 and 20 through 22 (Airborne Position) rate is 0.5 sec.
Type Code 19 (Airborne Velocity) rate is 0.5 sec.
Type Code 28 (Aircraft Status, e.g. emergency/priority) rate is 1.0 sec.
Type Code 31 (Aircraft Operational Status) rate is 1.7 sec.


text:
In RTCA DO-260B, what were the reasons GVA was added ? Is it a replacement for something?
After digging up and reading through many documents, I have a rough picture of the evolution of DO-260 versions, particularly for its ADS-B Quality Indicators. For instance, in DO-260 (Version 0) integrity & accuracy were expressed in a single parameter called Navigation Uncertainty Category (NUC). In DO-260A (Version 1), more quality indicators were added such as Navigation Integrity Category (NIC), Surveillance Integrity Level (SIL), Navigation Accuracy Category for Velocity and Position (NACv & NACp), and many more. In fact, there were a lot of new things introduced in this version. In DO-260B (Version 2), more were added such as SIL supplements, System Design Assurance (SDA), Geometric Design Assurance (GVA), and many more.
It is important to note that the majority of the quality indicators in DO-260A were reliant on vertical components. For example, NACp is derived from Horizontal Figure of Merit AND Vertical Figure of Merit, NIC and its Vertical Protection Level, NACv and its VFOM, etc. However, in DO-260B, the vertical components from the quality indicators were removed and a new parameter called GVA was added.
I found too little info on GVA. What I know is that GVA shall be set by using the Vertical Figure of Merit (VFOM) 95% from the GNSS position source used to encode the geometric altitude field in the ADS-B message. Thus, each number on Figure 1 has a meaning. I searched about VFOM and found a schematic of it (Figure 2). Would this be a valid representation of GVA?

Figure 1

Figure 2

Sources:
 Figure 1 : RTCA DO-260B DRAFT Version 4.2
 Figure 2 : GNSS Height on Airbus A/C, Slide 5
 1. Analysis of Quality Indicators in ADS-B Messages by Simon Tesi & Stainslav Pleninger
 2. Study on Airworthiness Requirement for the Position QUality of ADS-B System by YAN Fang

Welcome to [aviation.se], well done for your first question! I edited to label your pictures, please make sure I got them labeled correctly. Also, please [edit] to indicate the source of the images (as is policy here). Additionally, if you can provide some links to your sources of info on D-260x, many would find that helpful. While you're waiting for an answer, take the [tour] and browse through the [help] to learn how this Q&A board is different than most "discussion" forums - it'll help you get the most out of this site.

@FreeMan Ah yes, thank you for reminding me.

You don't have specific quotes, so that's about the best you can do for siting sources. Nicely done. Also, I'd expect another answer or two in the next day or so, but be sure to come back and give an up vote to the (currently) only answer and a check mark if you're finding it helpful. If/when more answers come along and you find one helps more, you can change the check mark later if you feel it's necessary/appropriate.

@FreeMan Noted. Thank you !

The philosophy behind the the quality indicators is that the ADS-B transmitting system sends the data it has, as well as information about the quality of that data. The receiving systems can then decide, based on the quality indicators, whether the data is good enough for their intended application.
The reason that more find grained quality indicators were developed in subsequent ADS-B versions had mainly to do with two factors:

new insights in the type of ADS-B applications were being developed
better performance and quality information delivered by GPS receivers

Note: at the time of DO-260 development, GPS had Selective Availability (SA) still turned on. This deliberately degraded the accuracy of the civilian GPS signal. This meant that both in the horizontal and the vertical plane the accuracy was very poor compared to current levels.
The big difference between version 0 (DO-260) and version 1 (DO-260A) was the split between accuracy (95% error under nominal conditions) and integrity (protection against non-nominal performance).
DO-260B then split the quality indicators between the horizontal and vertical component (hence the introduction of Geometric Vertical Accuracy (GVA)), added a finer grained resolution to horizontal position integrity and distinguished between between measurement integrity and avionics faults (the concept of system design assurance (SDA)).
GVA is intended for ADS-B applications that depend on the accuracy of the geometric vertical position. One such application is RVSM compliance monitoring using ADS-B. They compare the reported flight level to the geometric height from ADS-B, using an meteo model to compensate for the non-standard pressure distribution in the atmosphere. GVA helps to assess whether a potential mismatch between geometric and pressure altitude is caused by the baro altitude system, the meteo model or the GPS receiver.

The representation in your question shows a cylinder with hard boundaries to represent HFOM and VFOM. Whilst the numbers indeed define clear boundaries, it is important to understand that these are the statistical 95% level of the position errors, as estimated by the GPS receiver. This means that

position errors may occur that are outside of the cylinder (5% of the cases, if the estimate is correct)
the estimate may be (and usually is) wrong. Receivers tend to be conservative in estimating the position error magnitude.

Disclosure: I was involved in the international combined Working Group 51 / Special Committee 186 that wrote the ADS-B standards, however I joined at the time when the work on DO-260B was almost finished. At this moment I not involved anymore in ADS-B standardisation and implementation.

Thank you for your explanation as it helped me a lot for a research I am doing at the moment. When you said, "The big difference between version 0 (DO-260) and version 1 (DO-260A) was the split between accuracy (95% error under nominal conditions) and integrity (protection against non-nominal performance)." I am a bit confused on 95% error under nominal conditions. Did you mean 95% accuracy under normal conditions ?

Hi @Agha Indeed 95% accuracy

Hi@ DeltaLima please can you help me to understand MOPS and Quality indicators
Email: fahemoussama27@gmail.com thanks again

Hi @OussamaSDR , I am happy to help you. Just ask the right question here at StackExchange. In case you can't ask the question here due to confidentiality (which seem unlikely in case of the MOPS), you may contact me on LinkedIn (see my profile), occasionally I help out people directly.


text:
How fixed air, gas and fixed weights in rigid airships is computed in this book?
I hope I am posting this in the right forum. My current problem is part aviation, part maths.
I have been struggling with the following computation ( Burgess, Charles Paine. Airship Design. Honolulu, Hawaii: University Press of the Pacific, 2004. page 14. The pdf is available at http://www.xlta.org/library/burgess.pdf, note that the first edition of this book was written in 1927. The present snippet uses the typographical conventions from the pdf.)

Problem 1:
Find the volume and horsepower of a rigid airship to carry a military load of 15,000 lbs.at 60 knots (101.3 ft. / sec.). for 60 hours, 85% of the total volume being filled with helium lifting .064 lb./ft.**3 (94 % pure) in the standard atmosphere.
Since the hull is specified in the condition of the problem to be 85% full of gas,
the weight of the gas is 85% D multiplied by the difference between the weight of air and
the lift of gas per unit volume, and divided by the weight of air per unit volume. The total
weight of air and gas is therefore given:

$$
Air\; and\; gas = [ .15 + .85 ( .07635 - .064 ) / .07635 ] \times D = .288 D
$$
While this formula is not an issue, the subsequent formula has been giving me headaches.

From existing data, the fixed weights exclusive of power plant, power cars, and fuel system
equal -3D, and the crew, stores and ballast amount to .055 D. There remains for power plant, fuel, and military load

$$
( 1 - .288 - .30 - .055) D = .357 D
$$
Question is how did the author arrive at this result? Not matter how I approach solving the equation,
I am unable to get the same result. Problem is that the result of this equation is used at a later
stage. I also considered that 1 might be an i, but there was no mention of any constant i in the chapter this formula was taken from. I have no clue what I am missing here.

I agree the "1" can easily be mistaken with a "I", but I also think this is a "1". I'm glad now we can use modern tools to write equation and avoid such ambiguity.

A lower-case L "l" was often used as a substitute for the digit one "1" in early typography and typewriters. An off-topic anecdote: My father learned to type on a typewriter without a digit one key and this bit him hard when he was programming in the punch card days. He one spent spent 3 weeks chasing down a bug in a program because he'd used an "l" (ell) when he needed a "1" (one) and the compiler happily created a whole new variable for him. Lesson: always predeclare your variables and shun compilers that will create variables for you on the fly!

@FreeMan Thanks for your note on typography, that actually helps. Apart from dealing with all the math, the print is not great and although I've come across several "old" books with "strange" typography, trying to figure out variables in formulae makes it even harder. Luckily, pdf files can be magnified, another benefit of "the modern era" (not implying that everything is better now).

I think there is a typo in the second quote which initially threw me: -3D should be .30 D. BTW: I've read some of the old fluid dynamics books of the Saturn 5 era before modern CFD. Excellent read.

$D$ is the total displacement (the weight of the air displaced by the airship)
$0.288 \cdot D$ is the weight of helium and air inside the air ship
$0.055 \cdot D$ is the weight of crew, storage, and ballast
$x \cdot D$ is the unknown weight of power plants, power cars, and the fuel system
$0.3 \cdot D$ is anything else (fixed weights)

The total must be one:
$$.288 + .055 + .3 + x = 1$$
or equivalent, the total must be the displacement:
$$D \cdot (.288 + .055 + .3 + x) = 1 \cdot D$$
solve for x and you get:
$$x \cdot D = (1 - .288 - .055 - .3) \cdot D$$
or just
$$x = 1 - .288 - .055 - .3 = .357$$

Could it be that there is a typo in your formula. I think it should be 0.055 instead of 0.55 (cf. edit(s) above). I tried to edit it, but could not save the changes due to minimum amount of characters required. Anyway, I entered the formula in the calculator and got the result. Still can't tell why I wasn't able to compute this formula in the first place, since it is quite simple, maybe too simple.

Yes, indeed, thanks!


text:
why do Lycoming piston engine aircraft operate at 75% best power?
What happens to the remaining 25%, is the remaining 25% lost due to friction?

Your question needs clarification. Which Lycoming engine are you asking about? Why do you think it can only operate at 75% power?

Do you run your car's engine continuously at redline RPM?

Lycoming O-320-D3G. I'm asking why the POH says to operate at 75% best power and what are the reasons why its set at this percentage?

@BrainL sorry about the downvotes.  This is actually a good question if it  refers to the POH performance charts of a recreational aircraft with a piston engine such as a Cessna 172.  In cruising level flight  full throttle will be hopelessly fuel inefficient and may cause the aircraft to exceed safe speed limits.  Also, as you climb, 100% power cannot be generated due to thinner air.  So, reading your POH (+10 for that) keep in mind the performance envelope (Vne, Vsafe manuvering, Vflaps extended) and remember "55, 65, 75%" power at given altitudes is for TAS and gallons per hour cruising

If you climb, give it all you've got (watch for overheating, and density altitude).

This question has potential, and with an extensive rewrite, it could be a very good one. The OP's comment being incorporated would get it part-way there. But as it stands, it just isn't there. Voting to leave closed, but willing to re-open if further edits improve what's being asked.

No. Let's assume sea level operation. At 75% power, the engine is burning only 75% of its maximum fuel flow rate, and the remaining 25% of the engine capacity is "off line"- but available at any time by pushing the propeller speed control up to full fine pitch (for a plane with a constant-speed prop) or by opening the throttle all the way (in a plane with a prop fixed at fine pitch).
Note that depending on the engine it may be limited to full power for perhaps only three minutes total time, to prevent the engine from overheating. So you use full power for three minutes during takeoff and initial climbout and then pull the power back to cruise power at the 3-minute mark.

Light aircraft manufacturers typically use 75% power as a normal cruising power. There is really no set reason for this 75% figure. It is just a convenient convention that most light aircraft manufacturers use.
Part of the reason for this is that a normally aspirated (non-turbocharged) piston engine can only produce 100% rated power at sea level on a standard day. (15C and 29.92). This means that in most cases 100% rated power is not available for takeoff.